Chemical mechanical process (CMP), also know as chemical mechanical planarization or chemical mechanical polishing, has become a widely used technique for polishing certain work pieces. Particularly, the computer manufacturing industry has begun to rely heavily on CMP processes for polishing wafers of ceramics, silicon, glass, quartz, metals, and mixtures thereof for use in semiconductor fabrication. Such polishing processes generally entail applying the wafer against a rotating pad made from a durable organic substance such as polyurethane. Additionally, a slurry of a chemical solution capable of breaking down the wafer substance, and a sufficient amount of abrasive particles is added to the pad to further aid in the polishing of the wafer surface. The slurry is continually added to the rotating CMP pad, and the dual chemical and mechanical forces exerted on the wafer cause it to polish or planarize in a desired manner.
In a typical polishing process, the working surface of the pad holds the slurry containing the abrasive particles, usually by a mechanism such as fibers, asperities or small grooves, which provide a friction force sufficient to prevent the particles from being thrown off of the pad due to the centrifugal force exerted by the pad's spinning motion. Therefore, it is important to assure that there are an abundance of openings and grooves available on the pad surface to receive new slurry.
A problem with maintaining the working surface of the pad is caused by an accumulation of polishing debris coming from the work piece, abrasive slurry, and dressing disk. This accumulation causes a “glazing” effect, or hardening of the working surface of the pad, and wears or mats the fibers down. Thus, the pad is less able to hold the abrasive particles of the slurry, and the pad's overall polishing performance is significantly decreased. Further, with many pads, the grooves used to hold the slurry become clogged, and the pad's polishing surface becomes depressed and matted. Therefore, attempts have been made to revive the surface of the pad by “grooming” or “cutting” grooves and forming asperities on the surface with various devices. This process has come to be known as “grooming”, “dressing” or “conditioning” the CMP pad. Many types of devices and processes have been used for this purpose. One such device is a disk with a plurality of superabrasive particles, such as diamond particles, attached to a surface or substrate thereof.
There have been improvements in CMP pad dresser devices to enhance their conditioning properties and to improve the pad properties. However, these improvements have been met with limited success. For example, the present CMP pad dressers lack the ability to form asperities in the pad surface having uniform heights. Uniformity in asperity height can determine the polishing rate as well as polishing performance. Therefore, CMP pads which contain asperities having uniform height promote polished wafers having more planar surfaces; while pads having asperities that varying in height result in unreliable polishing rates and micro-size wafer surface deformities.
Yet another disadvantage with modern CMP processes is reduced life of the CMP pad and the abrasive particles on the CMP pad dresser. Abrasive particles and CMP pads can wear out prematurely when the particles remove more pad material than is necessary. With the CMP pad and abrasive particles wearing out prematurely, the high polishing rate and quality needed are lost and the ability to revitalize the pad surface is further reduced. In general, the polishing process pulls the abrasive particles through the pad surface while dragging the deformable pad material. Dragging the pad material promotes irregular and unpredictably sized asperities. Additionally, dragging the pad material places undue wear on the abrasive particles and, can cause premature wearing, thereby further creating an unpredictable polishing process.
In view of the foregoing, it is desirable to obtain methods and CMP pad dressers which can optimize CMP pad polishing performance while maximizing efficiency and lifespan of the CMP pad dresser.